Binaural processing is important because it allows organisms to localize sounds in their environment. Evidence of this processing can be found at early levels of central auditory pathways in mammals, including nuclei of the superior olive, lateral lemniscus, and inferior colliculus. Neurons in these pathways use interaural time and level differences (ITD's and ILD'S) to compute the source of a sound. Part of this processing involves the interaction of excitatory inputs driven by one ear and inhibitory inputs driven by the other ear. In this project we will investigate which neurons in the auditory pathways provide inhibitory inputs for binaural processing, and how these inputs converge with excitatory inputs at different levels of the auditory pathway. We will relate these findings to the processing of ITD's and ILD's in nuclei of the superior olive, lateral lemniscus, and inferior colliculus. To do this, immunocytochemistry and transmitter-specific uptake will be used to identify which neurons in the nuclei of the superior olive, lateral lemniscus, and inferior colliculus may use inhibitory or excitatory transmitters. These procedures will be combined with retrograde transport of exogenously injected tracers to identify inhibitory or excitatory neurons with ascending projections. Moreover, anterograde tracing of the afferent inputs to these projection neurons will be combined with retrograde transport and immunocytochemistry. In this way we will define the chains of neurons and their inhibitory connections which are likely to be involved in the binaural processing of ITD's and ILD'S.